Heretofore, the prevention of soil born plant diseases was very difficult and development of a good fungicide has been especially desired. For example, the damages of Cruciferous plants attacked by clubroot have been increasing year by year.
Clubroot is a very serious disease when susceptible varieties of any cruciferous species such as cauliflower, mustard, radish, cabbage, rape and turnip are grown in infested fields, and losses caused by it are sometimes very heavy. Fields once infested with the clubroot pathogen remain so indefinitely and become unfit for cultivation of crucifers practically forever or until costly methods and materials are used to sterilize the soil.
Various preventive measures by means of fungicide against the soil born plant diseases are actually tried, however, no satisfactory result is obtained with conventional medicines and thus these are not favorable for the practical use. Thus, at present, no satisfactory soil fungicide is commercially available because one fungicide has such disadvantages that no sufficient preventive effect is obtained thereby unless a high concentration of the fungicide is disposed and this results that the fungicide is liable to remain into the plant body and/or in the soil, another has a high toxicity to men and/or beasts, another has liable to cause a phytotoxity and another has an irritative smell or unpleasant odor.
For example, an environment pollution problem is caused because mercury compounds have a high toxicity and chloropicrin has toxicity and irritative smell.
The inventors have undertaken the research for developing a soil fungicide free of defects mentioned above and found the fact that the compounds of the formula (I) have shown a high prevention effect against the soil born plant diseases, especially having a distinguished effect against clubroot of Cruciferous plants even with a low concentration.